What is the molecular clock assumption?

What is the molecular clock assumption?

• A. The rate of genetic mutations is relatively constant over time.
• B. All genes mutate at the same rate in every lineage.
• C. Mutation rate is highly variable and unpredictable.
• D. Molecular clocks can only be calibrated with fossil dates.

Answer: (A)

Mutations accumulate at a roughly constant rate over time, so the number of genetic differences between two species can be used as a clock to estimate when they split. This means the clock is most reliable when the rate is stable enough that time can be inferred from the amount of change, especially for neutral mutations that don’t affect fitness. In practice, rates can vary among genes and lineages, so scientists use relaxed-clock models or other approaches to account for some variation. To convert those differences into actual years, researchers anchor the clock with independent time information, often fossil dates, but other calibration points can be used as well.

Mutations accumulate at a roughly constant rate over time, so the number of genetic differences between two species can be used as a clock to estimate when they split. This means the clock is most reliable when the rate is stable enough that time can be inferred from the amount of change, especially for neutral mutations that don’t affect fitness. In practice, rates can vary among genes and lineages, so scientists use relaxed-clock models or other approaches to account for some variation. To convert those differences into actual years, researchers anchor the clock with independent time information, often fossil dates, but other calibration points can be used as well.